Respiratory syncytial virus (RSV) plays an important role in the pathogenesis of acute otitis media. There is evidence that RSV can interact with respiratory epithelium and polymorphonuclear leukocytes (PMNs) to produce potentially deleterious mediators. However, the physiologic significance of this interaction is unknown. The proposed project is designed to investigate whether the respiratory epithelial cells, the target cells for RSV infection, can be the initial source of immunoreactive substances capable of modulating PMN adhesion; and whether activated PMNs contribute to both tissue injury and delayed bacterial clearance. We hypothesize that: I) middle ear epithelium infected with RSV produces immunoreactive substances capable of modulating PMN adhesion; II) PMNs adherent to RSV-infected epithelium injure the middle ear by releasing cytotoxic agents; III) cytotoxic agents released during RSV infection in turn inhibit elimination of invading bacteria by PMNs. These hypotheses will be tested by using in vitro respiratory epithelial cell cultures, clinical samples of middle ear fluids, and experimental animal models for the following specific aims: 1) The synthesis of proinflammatory mediators in RSV-infected respiratory epithelial cultures and their presence in clinical samples of middle ear fluids will be analyzed by enzyme linked immunoassays, radioimmunoassays and polymerase chain reaction. The effects of these mediators on PMN adhesion molecules and their ligands relative to PMN adherence to respiratory epithelium, will be studied by fluorescent activated flow cytometry, immunohistology, and visual adherence assays. 2) The effect of PMN adhesion to RSV infected epithelial cells relative to cell cytotoxicity will be examined in respiratory epithelial cell lines. 3) The effects of toxic oxygen radicals and possibly other agents produced by activated PMN in the RSV-infected middle ear on the ability of these PMNs to eliminate secondary invading bacteria will be analyzed by determination of the adherence, movement, phagocytosis, and oxidative metabolic capabilities of these altered PMNs. The results of these studies should help guide future evaluations of the use of antiviral vaccines and PMN modulators in otitis media.